System and method for obtaining certificate status of subkeys

ABSTRACT

Systems and methods for updating status of digital certificate subkeys. A request is made to a key server to verify if a given key is revoked. If it is not, then the key with its subkeys is acquired from the key server. If one or more subkeys or signatures of the subkeys are different in the acquired key, then the key is replaced.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to and the benefit of U.S. ProvisionalApplication Serial No. 60/567,162, filed on Apr. 30, 2004, of which theentire disclosure (including any and all figures) is incorporated hereinby reference.

TECHNICAL FIELD

This document relates generally to the field of communications, and inparticular to obtaining certificate status of subkeys on computingdevices.

BACKGROUND

Many security systems rely on digital certificates or “keys” forencryption and authentication of a message. The terms “key,” “main key,”“certificate,” and “digital certificate” are used interchangeablythroughout this document and can mean a digital credential whichincludes a public key, for encrypting information directed to the userof the key and information for authenticating the user.

Some security systems, such as Pretty Good Privacy (PGP), do notimplement a centralized authority (which keeps the most up to datestatus of all keys on that system, and distributes certificaterevocation lists, indicating which certificates have been revoked).Instead, PGP implements “a web of trust,” a method where other entities,other than a centralized authority, authenticate the keys by “signing”them. Other users may or may not consider a key authentic depending onthe combination of entities which signed a given key.

PGP allows keys to be stored on key servers. The owner of a key maychange the status of his key on a server, for example, the owner mayrevoke the key. Also other users may change the status of the key bysigning it or removing their signature. A user on such system who hasobtained a key of another user from the server for the purposes ofencryption and authentication, has to manually download and verify thekey to determine that it has not been revoked by the owner and that itcan still be trusted based on combination of signatures associated withit.

SUMMARY

In accordance with the teachings provided herein, systems and methodsfor operation upon data processing devices are provided in order toovercome one or more of the aforementioned disadvantages or otherdisadvantages concerning the handling of digital keys processing. Forexample, a system and method can be configured to automatically acquirekeys, which are already on the device, from a key server, verify theirstatus, and update the key on this or other devices, if the status haschanged. Aspects of the systems and methods can be implemented oncomputer-readable media as well as through data signals which conveyinformation from and/or to the systems.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram illustrating an exemplary communicationnetwork in which a mobile wireless device may be used;

FIG. 2 is a block diagram illustrating alternative paths of providinginformation to a mobile wireless device;

FIG. 3 is a block diagram illustrating the use of a message server toobtain certificate status of one or more subkeys.

FIG. 4 is a block diagram illustrating communications between a mobiledevice and a key server in order to obtain certificate status of one ormore subkeys.

FIG. 5 is a flowchart illustrating steps involved in updatingcertificate status of subkeys;

FIG. 6 is a block diagram illustrating an exemplary implementation of amobile wireless device.

DETAILED DESCRIPTION OF THE EMBODIMENTS

FIG. 1 is an overview of an example communication system in which awireless communication device may be used. One skilled in the art willappreciate that there may be hundreds of different topologies, but thesystem shown in FIG. 1 helps demonstrate the operation of the encodedmessage processing systems and methods described in the presentapplication. There may also be many message senders and recipients. Thesimple system shown in FIG. 1 is for illustrative purposes only, andshows perhaps the most prevalent Internet e-mail environment wheresecurity is not generally used.

FIG. 1 shows an e-mail sender 10, the Internet 20, a message serversystem 40, a wireless gateway 85, wireless infrastructure 90, a wirelessnetwork 105 and a mobile communication device 100.

An e-mail sender system 10 may, for example, be connected to an ISP(Internet Service Provider) on which a user of the system 10 has anaccount, located within a company, possibly connected to a local areanetwork (LAN), and connected to the Internet 20, or connected to theInternet 20 through a large ASP (application service provider) such asAmerica Online (AOL). Those skilled in the art will appreciate that thesystems shown in FIG. 1 may instead be connected to a wide area network(WAN) other than the Internet, although e-mail transfers are commonlyaccomplished through Internet-connected arrangements as shown in FIG. 1.

The message server 40 may be implemented, for example, on a networkcomputer within the firewall of a corporation, a computer within an ISPor ASP system or the like, and acts as the main interface for e-mailexchange over the Internet 20. Although other messaging systems mightnot require a message server system 40, a mobile device 100 configuredfor receiving and possibly sending e-mail will normally be associatedwith an account on a message server. Perhaps the two most common messageservers are Microsoft Exchange™ and Lotus Domino™. These products areoften used in conjunction with Internet mail routers that route anddeliver mail. These intermediate components are not shown in FIG. 1, asthey do not directly play a role in the secure message processingdescribed below. Message servers such as server 40 typically extendbeyond just e-mail sending and receiving; they also include dynamicdatabase storage engines that have predefined database formats for datalike calendars, to-do lists, task lists, e-mail and documentation.

The wireless gateway 85 and infrastructure 90 provide a link between theInternet 20 and wireless network 105. The wireless infrastructure 90determines the most likely network for locating a given user and tracksthe user as they roam between countries or networks. A message is thendelivered to the mobile device 100 via wireless transmission, typicallyat a radio frequency (RF), from a base station in the wireless network105 to the mobile device 100. The particular network 105 may bevirtually any wireless network over which messages may be exchanged witha mobile communication device.

As shown in FIG. 1, a composed e-mail message 15 is sent by the e-mailsender 10, located somewhere on the Internet 20. This message 15 isnormally fully in the clear and uses traditional Simple Mail TransferProtocol (SMTP), RFC822 headers and Multipurpose Internet Mail Extension(MIME) body parts to define the format of the mail message. Thesetechniques are all well known to those skilled in the art. The message15 arrives at the message server 40 and is normally stored in a messagestore. Most known messaging systems support a so-called “pull” messageaccess scheme, wherein the mobile device 100 must request that storedmessages be forwarded by the message server to the mobile device 100.Some systems provide for automatic routing of such messages which areaddressed using a specific e-mail address associated with the mobiledevice 100. In a preferred embodiment described in further detail below,messages addressed to a message server account associated with a hostsystem such as a home computer or office computer which belongs to theuser of a mobile device 100 are redirected from the message server 40 tothe mobile device 100 as they are received.

Regardless of the specific mechanism controlling the forwarding ofmessages to the mobile device 100, the message 15, or possibly atranslated or reformatted version thereof, is sent to the wirelessgateway 85. The wireless infrastructure 90 includes a series ofconnections to wireless network 105. These connections could beIntegrated Services Digital Network (ISDN), Frame Relay or T1connections using the TCP/IP protocol used throughout the Internet. Asused herein, the term “wireless network” is intended to include threedifferent types of networks, those being (1) data-centric wirelessnetworks, (2) voice-centric wireless networks and (3) dual-mode networksthat can support both voice and data communications over the samephysical base stations. Combined dual-mode networks include, but are notlimited to, (1) Code Division Multiple Access (CDMA) networks, (2) theGroupe Special Mobile or the Global System for Mobile Communications(GSM) and the General Packet Radio Service (GPRS) networks, and (3)future third-generation (3G) networks like Enhanced Data-rates forGlobal Evolution (EDGE) and Universal Mobile Telecommunications Systems(UMTS). Some older examples of data-centric network include the Mobitex™Radio Network and the DataTAC™ Radio Network. Examples of oldervoice-centric data networks include Personal Communication Systems (PCS)networks like GSM, and TDMA systems.

FIG. 2 is a block diagram of a further example communication systemincluding multiple networks and multiple mobile communication devices.The system of FIG. 2 is substantially similar to the FIG. 1 system, butincludes a host system 30, a redirection program 45, a mobile devicecradle 65, a wireless virtual private network (VPN) router 75, anadditional wireless network 110 and multiple mobile communicationdevices 100. As described above in conjunction with FIG. 1, FIG. 2represents an overview of a sample network topology. Although theencoded message processing systems and methods described herein may beapplied to networks having many different topologies, the network ofFIG. 2 is useful in understanding an automatic e-mail redirection systemmentioned briefly above.

The central host system 30 will typically be a corporate office or otherLAN, but may instead be a home office computer or some other privatesystem where mail messages are being exchanged. Within the host system30 is the message server 40, running on some computer within thefirewall of the host system, that acts as the main interface for thehost system to exchange e-mail with the Internet 20. In the system ofFIG. 2, the redirection program 45 enables redirection of data itemsfrom the server 40 to a mobile communication device 100. Although theredirection program 45 is shown to reside on the same machine as themessage server 40 for ease of presentation, there is no requirement thatit must reside on the message server. The redirection program 45 and themessage server 40 are designed to co-operate and interact to allow thepushing of information to mobile devices 100. In this installation, theredirection program 45 takes confidential and non-confidential corporateinformation for a specific user and redirects it out through thecorporate firewall to mobile devices 100. A more detailed description ofthe redirection software 45 may be found in the commonly assigned U.S.Pat. No. 6,219,694 (“the '694 Patent”), entitled “System and Method forPushing Information From A Host System To A Mobile Data CommunicationDevice Having A Shared Electronic Address”, and issued to the assigneeof the instant application on Apr.17, 2001, which is hereby incorporatedinto the present application by reference. This push technique may use awireless friendly encoding, compression and encryption technique todeliver all information to a mobile device, thus effectively extendingthe security firewall to include each mobile device 100 associated withthe host system 30.

As shown in FIG. 2, there may be many alternative paths for gettinginformation to the mobile device 100. One method for loading informationonto the mobile device 100 is through a port designated 50, using adevice cradle 65. This method tends to be useful for bulk informationupdates often performed at initialization of a mobile device 100 withthe host system 30 or a computer 35 within the system 30. The other mainmethod for data exchange is over-the-air using wireless networks todeliver the information. As shown in FIG. 2, this may be accomplishedthrough a wireless VPN router 75 or through a traditional Internetconnection 95 to a wireless gateway 85 and a wireless infrastructure 90,as described above. The concept of a. wireless VPN router 75 is new inthe wireless industry and implies that a VPN connection could beestablished directly through a specific wireless network 110 to a mobiledevice 100. The possibility of using a wireless VPN router 75 has onlyrecently been available and could be used when the new Internet Protocol(IP) Version 6 (IPV6) arrives into IP-based wireless networks. This newprotocol will provide enough IP addresses to dedicate an IP address toevery mobile device 100 and thus make it possible to push information toa mobile device 100 at any time. A principal advantage of using thiswireless VPN router 75 is that it could be an off-the-shelf VPNcomponent, thus it would not require a separate wireless gateway 85 andwireless infrastructure 90 to be used. A VPN connection would preferablybe a Transmission Control Protocol (TCP)/IP or User Datagram Protocol(UDP)/IP connection to deliver the messages directly to the mobiledevice 100. If a wireless VPN 75 is not available then a link 95 to theInternet 20 is the most common connection mechanism available and hasbeen described above.

In the automatic redirection system of FIG. 2, a composed e-mail message15 leaving the e-mail sender 10 arrives at the message server 40 and isredirected by the redirection program 45 to the mobile device 100. Asthis redirection takes place the message 15 is re-enveloped, asindicated at 80, and a possibly proprietary compression and encryptionalgorithm can then be applied to the original message 15. In this way,messages being read on the mobile device 100 are no less secure than ifthey were read on a desktop workstation such as 35 within the firewall.All messages exchanged between the redirection program 45 and the mobiledevice 100 preferably use this message repackaging technique. Anothergoal of this outer envelope is to maintain the addressing information ofthe original message except the sender's and the receiver's address.This allows reply messages to reach the appropriate destination, andalso allows the “from” field to reflect the mobile user's desktopaddress. Using the user's e-mail address from the mobile device 100allows the received message to appear as though the message originatedfrom the user's desktop system 35 rather than the mobile device 100.

With reference back to the port 50 and cradle 65 connectivity to themobile device 100, this connection path offers many advantages forenabling one-time data exchange of large items. For those skilled in theart of personal digital assistants (PDAs) and synchronization, the mostcommon data exchanged over this link is Personal Information Management(PIM) data 55. When exchanged for the first time this data tends to belarge in quantity, bulky in nature and requires a large bandwidth to getloaded onto the mobile device 100 where it can be used on the road. Thisserial link may also be used for other purposes, including setting up aprivate security key 111 such as an S/MIME or PGP specific private key,the Certificate (Cert) of the user and their Certificate RevocationLists (CRLs) 60. The private key is preferably exchanged so that thedesktop 35 and mobile device 100 share one personality and one methodfor accessing all mail. The Cert and CRLs are normally exchanged oversuch a link because they represent a large amount of the data that isrequired by the device for S/MIME, PGP and other public key securitymethods.

FIG. 3 is a block diagram illustrating communications with a key server160 in order to obtain certificate status of one or more subkeys for agiven certificate. The message server 40 can be configured toautomatically determine the time when to verify the status of subkeys(172 a, 172 b, 172 c). The subkeys (172 a, 172 b, 172 c) are associatedwith a key 170 the server has previously downloaded. The mobile wirelessdevice 100 has a copy of this key 170 with the subkeys (172 a, 172 b,172 c), in order to be able to read and send messages using a “web oftrust” security type system, such as PGP.

The message server 40 sends a status request 162 for the key 170 to thekey server 160. The key server 160 sends response 164 back to themessage server 40, which contains the information on whether the key 170has been revoked by its user. If it has been revoked, then the messageserver 40 notifies the wireless mobile device 100 about the revocation.

If the key 170 has not been revoked, then the message server 40 sends arequest 166 for the key 170 with its subkeys to the key server 160. Thekey server 160 sends a response 168 with the current version of the keywith its subkeys and signatures. Once the message server 40 receives themost recent version of the key, it compares it to the version that ithad before. If the message server 40 detects a difference between theversion of the key, it replaces the old version with the new version,and sends a message 174 to the mobile device 100 with the entire key.The mobile device 100 receives the message 174, and replaces its copy ofthe key with the new version. After the key is replaced on the mobiledevice 100, a notification 154 can be sent to the user of the mobiledevice 100. In the end, the subkey which has changed can be replaced onboth devices without the user's involvement.

The message server 40 may be configured in many different ways, such asto send to the mobile device 100 only subkeys, which have changed, andnot the entire key. The message server 40 can include a softwarecomponent which could interpret the structure of the keys and identifywhich subkey(s) have changed. Sending only the changed subkeys, insteadof the entire key (with the subkeys which did not change) can savebandwidth on the wireless link. The verification of the subkey statusmay be initiated by a user or automatically initiated according to apredefined schedule contained on the mobile device 100 or the messageserver 40. In some embodiments, the schedule may be periodic with aperiod, for example, of one day.

FIG. 3 depicts the message server 40 communicating with a key server160. However as shown at 180 in FIG. 4, the mobile device 100 can beconfigured to communicate with the key server 160 directly. The mobiledevice 100 may bypass the message server 40 to communicate directly withthe key server 160, or may be configured to allow some of thecommunications to occur through the message server 40 with the remainingcommunications occurring through a direct connection 180 over a wirelessnetwork 182 with the key server 160.

FIG. 5 depicts an operational scenario for obtaining certificate statusof a PGP subkey. In this operational scenario, it is possible in PGP touse different keys for encryption and authentication. Subkeys may beused for encryption and the main key may be used for authentication.

A user may create any number of subkeys for his main key. For example,if the main key is valid for three years, three subkey may be created tobe valid for only one year each. This reduces the amount of ciphertexton the Internet encrypted with the same key (or subkey), thereby,reducing the opportunity for an attacker to determine the private key ofthe user. Keys and their subkeys are stored on the key server, wherethey are uploaded by owners and signers.

When keys and/or subkeys are used to encrypt and/or authenticate amessage, the receiver of the message downloads the key for a sender ofthe message from the key server for authentication of the incomingmessages from that user and for encryption of outgoing messages to thatuser. Once the receiver of the message determines, based on thesignatures, that the main key used to sign the incoming message isauthentic, he can be sure that the sender of the message is not anattacker. Also, when sending a message to another user, his subkey maybe used for encryption. The subkey is a part of the receiver's main key,and its authenticity can be verified, based on signatures, beforesending the message.

Once the key and subkeys have been acquired for the first time, they maychange on the key server without a user knowing. A message server canmake a request to verify the status for a given key using LightweightDirectory Access Protocol (LDAP). The key server sends a responsenotifying the message server whether the key is revoked or not. However,if the message server wishes to update the certificate status forsubkeys of the main PGP key (whether user or program initiated), thencode on the device downloads as indicated at step 200 the PGP key inwhich the subkey is contained. At step 202, the signatures of thedownloaded subkey are compared to what is present on the device. At step205, if the signatures have changed, then the device copy is updated tobe consistent with the downloaded copy. If the subkey has been revoked(or has changed), then the user can be alerted at step 206.

The method of FIG. 5 can be utilized on an e-mail server that handlesmessages for the mobile device, or the method can be performed on themobile device, or the different steps can be distributed across both theserver and the mobile device depending upon the situation at hand.

The verification approach of the example operational scenario seamlesslydetermines for the user the status of the subkey for the user. It isnoted that because of the significant differences between PGP andS/MIME, such as PGP's use of a web of trust model, a mobile device canutilize the methods and systems disclosed herein to fetch thecertificate status of PGP subkeys.

The systems and methods disclosed herein are presented only by way ofexample and are not meant to limit the scope of the invention. Othervariations of the systems and methods described above will be apparentto those skilled in the art and as such are considered to be within thescope of the invention which is defined by claims. For example, itshould be understood that the steps and the order of the steps in theflowchart described herein may be altered, modified and/or augmented andstill achieve the desired outcome.

As another example, the disclosed verification processing approachescould be extended in many ways, such as fetching the status of the mainPGP key. When a signature is being updated, conflicts could arisebecause the owner of the key may have revoked the key, but the user'ssignature may disagree with that. The user is then prompted to determinewhat course of action to take. Alternatively, the code couldautomatically choose the appropriate path (either based on security orbased on keeping the status quo with respect to the key) and decidewhether to accept the revocation or not.

Still further, the systems and methods disclosed herein may be used withmany different computers and devices, such as a wireless mobilecommunications device shown in FIG. 6. With reference to FIG. 6, themobile device 100 is a dual-mode mobile device and includes atransceiver 311, a microprocessor 338, a display 322, non-volatilememory 324, random access memory (RAM) 326, one or more auxiliaryinput/output (I/O) devices 328, a serial port 330, a keyboard 332, aspeaker 334, a microphone 336, a short-range wireless communicationssub-system 340, and other device sub-systems 342.

The transceiver 311 includes a receiver 312, a transmitter 314, antennas316 and 318, one or more local oscillators 313, and a digital signalprocessor (DSP) 320. The antennas 316 and 318 may be antenna elements ofa multiple-element antenna, and are preferably embedded antennas.However, the systems and methods described herein are in no wayrestricted to a particular type of antenna, or even to wirelesscommunication devices.

The mobile device 100 is preferably a two-way communication devicehaving voice and data communication capabilities. Thus, for example, themobile device 100 may communicate over a voice network, such as any ofthe analog or digital cellular networks, and may also communicate over adata network. The voice and data networks are depicted in FIG. 6 by thecommunication tower 319. These voice and data networks may be separatecommunication networks using separate infrastructure, such as basestations, network controllers, etc., or they may be integrated into asingle wireless network.

The transceiver 311 is used to communicate with the network 319, andincludes the receiver 312, the transmitter 314, the one or more localoscillators 313 and the DSP 320. The DSP 320 is used to send and receivesignals to and from the transceivers 316 and 318, and also providescontrol information to the receiver 312 and the transmitter 314. If thevoice and data communications occur at a single frequency, orclosely-spaced sets of frequencies, then a single local oscillator 313may be used in conjunction with the receiver 312 and the transmitter314. Alternatively, if different frequencies are utilized for voicecommunications versus data communications for example, then a pluralityof local oscillators 313 can be used to generate a plurality offrequencies corresponding to the voice and data networks 319.Information, which includes both voice and data information, iscommunicated to and from the transceiver 311 via a link between the DSP320 and the microprocessor 338.

The detailed design of the transceiver 311, such as frequency band,component selection, power level, etc., will be dependent upon thecommunication network 319 in which the mobile device 100 is intended tooperate. For example, a mobile device 100 intended to operate in a NorthAmerican market may include a transceiver 311 designed to operate withany of a variety of voice communication networks, such as the Mobitex orDataTAC mobile data communication networks, AMPS, TDMA, CDMA, PCS, etc.,whereas a mobile device 100 intended for use in Europe may be configuredto operate with the GPRS data communication network and the GSM voicecommunication network. Other types of data and voice networks, bothseparate and integrated, may also be utilized with a mobile device 100.

Depending upon the type of network or networks 319, the accessrequirements for the mobile device 100 may also vary. For example, inthe Mobitex and DataTAC data networks, mobile devices are registered onthe network using a unique identification number associated with eachmobile device. In GPRS data networks, however, network access isassociated with a subscriber or user of a mobile device. A GPRS devicetypically requires a subscriber identity module (“SIM”), which isrequired in order to operate a mobile device on a GPRS network. Local ornon-network communication functions (if any) may be operable, withoutthe SIM device, but a mobile device will be unable to carry out anyfunctions involving communications over the data network 319, other thanany legally required operations, such as ‘911’ emergency calling.

After any required network registration or activation procedures havebeen completed, the mobile device 100 may the send and receivecommunication signals, including both voice and data signals, over thenetworks 319. Signals received by the antenna 316 from the communicationnetwork 319 are routed to the receiver 312, which provides for signalamplification, frequency down conversion, filtering, channel selection,etc., and may also provide analog to digital conversion. Analog todigital conversion of the received signal allows more complexcommunication functions, such as digital demodulation and decoding to beperformed using the DSP 320. In a similar manner, signals to betransmitted to the network 319 are processed, including modulation andencoding, for example, by the DSP 320 and are then provided to thetransmitter 314 for digital to analog conversion, frequency upconversion, filtering, amplification and transmission to thecommunication network 319 via the antenna 318.

In addition to processing the communication signals, the DSP 320 alsoprovides for transceiver control. For example, the gain levels appliedto communication signals in the receiver 312 and the transmitter 314 maybe adaptively controlled through automatic gain control algorithmsimplemented in the DSP 320. Other transceiver control algorithms couldalso be implemented in the DSP 320 in order to provide moresophisticated control of the transceiver 311.

The microprocessor 338 preferably manages and controls the overalloperation of the mobile device 100. Many types of microprocessors ormicrocontrollers could be used here, or, alternatively, a single DSP 320could be used to carry out the functions of the microprocessor 338.Low-level communication functions, including at least data and voicecommunications, are performed through the DSP 320 in the transceiver311. Other, high-level communication applications, such as a voicecommunication application 324A, and a data communication application324B may be stored in the non-volatile memory 324 for execution by themicroprocessor 338. For example, the voice communication module 324A mayprovide a high-level user interface operable to transmit and receivevoice calls between the mobile device 100 and a plurality of other voiceor dual-mode devices via the network 319. Similarly, the datacommunication module 324B may provide a high-level user interfaceoperable for sending and receiving data, such as e-mail messages, files,organizer information, short text messages, etc., between the mobiledevice 100 and a plurality of other data devices via the networks 319.

The microprocessor 338 also interacts with other device subsystems, suchas the display 322, the RAM 326, the auxiliary input/output (I/O)subsystems 328, the serial port 330, the keyboard 332, the speaker 334,the microphone 336, the short-range communications subsystem 340 and anyother device subsystems generally designated as 342.

Some of the subsystems shown in FIG. 6 perform communication-relatedfunctions, whereas other subsystems may provide “resident” or on-devicefunctions. Notably, some subsystems, such as the keyboard 332 and thedisplay 322 may be used for both communication-related functions, suchas entering a text message for transmission over a data communicationnetwork, and device-resident functions such as a calculator or task listor other PDA type functions.

Operating system software used by the microprocessor 338 is preferablystored in a persistent store such as non-volatile memory 324. Thenon-volatile memory 324 may be implemented, for example, as a Flashmemory component, or as battery backed-up RAM. In addition to theoperating system, which controls low-level functions of the mobiledevice 310, the non-volatile memory 324 includes a plurality of softwaremodules 324A-324N that can be executed by the microprocessor 338 (and/orthe DSP 320), including a voice communication module 324A, a datacommunication module 324B, and a plurality of other operational modules324N for carrying out a plurality of other functions. These modules areexecuted by the microprocessor 338 and provide a high-level interfacebetween a user and the mobile device 100. This interface typicallyincludes a graphical component provided through the display 322, and aninput/output component provided through the auxiliary I/O 328, keyboard332, speaker 334, and microphone 336. The operating system, specificdevice applications or modules, or parts thereof, may be temporarilyloaded into a volatile store, such as RAM 326 for faster operation.Moreover, received communication signals may also be temporarily storedto RAM 326, before permanently writing them to a file system located ina persistent store such as the Flash memory 324.

An exemplary application module 324N that may be loaded onto the mobiledevice 100 is a personal information manager (PIM) application providingPDA functionality, such as calendar events, appointments, and taskitems. This module 324N may also interact with the voice communicationmodule 324A for managing phone calls, voice mails, etc., and may alsointeract with the data communication module for managing e-mailcommunications and other data transmissions. Alternatively, all of thefunctionality of the voice communication module 324A and the datacommunication module 324B may be integrated into the PIM module.

The non-volatile memory 324 preferably also provides a file system tofacilitate storage of PIM data items on the device. The PIM applicationpreferably includes the ability to send and receive data items, eitherby itself, or in conjunction with the voice and data communicationmodules 324A, 324B, via the wireless networks 319. The PIM data itemsare preferably seamlessly integrated, synchronized and updated, via thewireless networks 319, with a corresponding set of data items stored orassociated with a host computer system, thereby creating a mirroredsystem for data items associated with a particular user.

Context objects representing at least partially decoded data items, aswell as fully decoded data items, are preferably stored on the mobiledevice 100 in a volatile and non-persistent store such as the RAM 326.Such information may instead be stored in the non-volatile memory 324,for example, when storage intervals are relatively short, such that theinformation is removed from memory soon after it is stored. However,storage of this information in the RAM 326 or another volatile andnon-persistent store is preferred, in order to ensure that theinformation is erased from memory when the mobile device 100 losespower. This prevents an unauthorized party from obtaining any storeddecoded or partially decoded information by removing a memory chip fromthe mobile device 100, for example.

The mobile device 100 may be manually synchronized with a host system byplacing the device 100 in an interface cradle, which couples the serialport 330 of the mobile device 100 to the serial port of a computersystem or device. The serial port 330 may also be used to enable a userto set preferences through an external device or software application,or to download other application modules 324N for installation. Thiswired download path may be used to load an encryption key onto thedevice, which is a more secure method than exchanging encryptioninformation via the wireless network 319. Interfaces for other wireddownload paths may be provided in the mobile device 100, in addition toor instead of the serial port 330. For example, a USB port would providean interface to a similarly equipped personal computer.

Additional application modules 324N may be loaded onto the mobile device100 through the networks 319, through an auxiliary I/O subsystem 328,through the serial port 330, through the short-range communicationssubsystem 340, or through any other suitable subsystem 342, andinstalled by a user in the non-volatile memory 324 or RAM 326. Suchflexibility in application installation increases the functionality ofthe mobile device 100 and may provide enhanced on-device functions,communication-related functions, or both. For example, securecommunication applications may enable electronic commerce functions andother such financial transactions to be performed using the mobiledevice 100.

When the mobile device 100 is operating in a data communication mode, areceived signal, such as a text message or a web page download, isprocessed by the transceiver module 311 and provided to themicroprocessor 338, which preferably further processes the receivedsignal in multiple stages as described above, for eventual output to thedisplay 322, or, alternatively, to an auxiliary I/O device 328. A userof mobile device 100 may also compose data items, such as e-mailmessages, using the keyboard 332, which is preferably a completealphanumeric keyboard laid out in the QWERTY style, although otherstyles of complete alphanumeric keyboards such as the known DVORAK stylemay also be used. User input to the mobile device 100 is furtherenhanced with a plurality of auxiliary I/O devices 328, which mayinclude a thumbwheel input device, a touchpad, a variety of switches, arocker input switch, etc. The composed data items input by the user maythen be transmitted over the communication networks 319 via thetransceiver module 311.

When the mobile device 100 is operating in a voice communication mode,the overall operation of the mobile device is substantially similar tothe data mode, except that received signals are preferably be output tothe speaker 334 and voice signals for transmission are generated by amicrophone 336. Alternative voice or audio I/O subsystems, such as avoice message recording subsystem, may also be implemented on the mobiledevice 100. Although voice or audio signal output is preferablyaccomplished primarily through the speaker 334, the display 322 may alsobe used to provide an indication of the identity of a calling party, theduration of a voice call, or other voice call related information. Forexample, the microprocessor 338, in conjunction with the voicecommunication module and the operating system software, may detect thecaller identification information of an incoming voice call and displayit on the display 322.

A short-range communications subsystem 340 is also included in themobile device 100. The subsystem 340 may include an infrared device andassociated circuits and components, or a short-range RF communicationmodule such as a Bluetooth™ module or an 802.11 module, for example, toprovide for communication with similarly-enabled systems and devices.Those skilled in the art will appreciate that “Bluetooth” and “802.11”refer to sets of specifications, available from the Institute ofElectrical and Electronics Engineers, relating to wireless personal areanetworks and wireless local area networks, respectively.

The systems' and methods' data may be stored in one or more data stores.The data stores can be of many different types of storage devices andprogramming constructs, such as RAM, ROM, Flash memory, programming datastructures, programming variables, etc. It is noted that data structuresdescribe formats for use in organizing and storing data in databases,programs, memory, or other computer-readable media for use by a computerprogram.

The systems and methods may be provided on many different types ofcomputer-readable media including computer storage mechanisms (e.g.,CD-ROM, diskette, RAM, flash memory, computer's hard drive, etc.) thatcontain instructions for use in execution by a processor to perform themethods' operations and implement the systems described herein.

The computer components, software modules, functions and data structuresdescribed herein may be connected directly or indirectly to each otherin order to allow the flow of data needed for their operations. It isalso noted that a module or processor includes but is not limited to aunit of code that performs a software operation, and can be implementedfor example as a subroutine unit of code, or as a software function unitof code, or as an object (as in an objected-oriented paradigm), or as anapplet, or in a computer script language, or as another type of computercode.

1. A method for operation upon one or more data processors for updatinga subkey in a web of trust security environment, comprising: determiningwhether a main key that is used within the security environment is notrevoked; acquiring the main key from a key server if the main key is notrevoked; updating main key if one or more signatures of one or moresubkeys is different in the acquired main key from the main key storedon a mobile device or a message server; wherein the one or more subkeysare associated with the main key for handling encryption of data withinthe web of trust security environment; issuing a notification if theearlier acquired main key is updated.
 2. The method of claim 1, whereinthe security environment does not include a centralized authority tostore current status of security-related keys; wherein key revocationinformation is not automatically distributed by a key server; whereinthe security environment allows users to determine whether a key isauthentic depending on combination of entities which signed a given key.3. The method of claim 2, wherein the main key and the one or moresubkeys are used within a Pretty Good Privacy security environment;wherein the one or more subkeys are used for encryption and can bedigitally signed by any user within the security environment.
 4. Themethod of claim 1, wherein determination of whether to update a main keyis performed according to a predetermined schedule.
 5. The method ofclaim 1, wherein determination of whether to update a main key isperformed due to a user initiated action.
 6. The method of claim 1,wherein the step of updating further comprises: sending a newly acquiredkey to a remote system.
 7. The method of claim 6, wherein the remotedevice is a wireless mobile communication device.
 8. The method of claim7, wherein the step of updating further comprises: sending to thewireless mobile communication device only subkeys whose set ofsignatures has changed.
 9. The method of claim 8, wherein a user of thewireless mobile communications device is prompted when a conflict hasarisen based upon an owner of the main key having revoked the main key;wherein the user is prompted to determine what course of action is to betaken with respect to the conflict.
 10. The method of claim 8, whereinwhen a conflict has arisen based upon the owner of the main key havingrevoked the main key, computer instructions automatically determine whatcourse of action is to be taken with respect to the conflict.
 11. Datasignals that are transmitted by the method of claim 1 using a computernetwork, wherein the data signals include: a request to the key serverfor a status of the main key, a response from the key server with astatus of the main key, a request to the key server for the main key, aresponse from the key server with the main key, and an update to aremote device with the main key; wherein the data signal is packetizeddata that is transmitted through a carrier wave across the network. 12.Computer-readable medium capable of causing a message server to performthe method of claim
 1. 13. Computer-readable medium capable of causing amobile wireless communications device to perform the method of claim 1.14. A system for operation upon one or more data processors for updatinga subkey in a web of trust security environment, comprising: dataprocessing instructions configured to determine whether main key of auser is not revoked; data processing instructions configured to acquirethe main key from a key server if the main key is not revoked; dataprocessing instructions configured to update main key of the user if oneor more signatures of one or more subkeys is different in the acquiredmain key from the main key stored on a mobile device; wherein the one ormore subkeys are associated with the main key for handling encryption ofthe user's data within the web of trust security environment; dataprocessing instructions configured to issue a notification if theearlier acquired main key is updated.
 15. The system of claim 14,wherein the data processing instructions are configured to operate upona message server, a mobile device, and combinations thereof.
 16. Asystem for operation upon one or more data processors for updating asubkey in a web of trust security environment, comprising: means foracquiring a main key from a key server; means for determining whetherone or more signatures of one or more subkeys is different in theacquired main key from the main key used by a mobile device; wherein theone or more subkeys are associated with the main key for handlingencryption of the user's data within the web of trust securityenvironment; means for updating main key of a user based upon resultfrom means for determining.